Rotogravure (Roto or Gravure for short) is a type of printing process that involves engraving the image on to an image carrier. In gravure printing, the image is engraved onto a cylinder because it uses a rotary printing press. Once a staple of newspaper photo features, the rotogravure process is still used for the commercial printing of magazines, postcards, and the printing of cardboard product packaging.
The general principles in offset lithography are identical to traditional metal plate lithography. The difference between them is in the manner by which they are printed. Various offset printing presses may have different roller systems but all share three major components: a plate cylinder that holds the printing plate, a blanket cylinder wrapped in rubber that carries the image to be transferred, and the impression cylinder which applies the pressure to print the image. A gear train connects all three cylinders together so they are in perfect synchrony with one another. Printing begins when a processed litho-plate containing an image is mounted on a cylinder, mechanically dampened with a wetting agent, and then rolled with ink. The oily ink is repelled from the damp areas and is attracted to the dry image areas. A blanket cylinder is then rolled over it, picking up the inky image onto its soft rubber surface. Paper then passes between this blanket cylinder and the hard impression cylinder, which presses all three surfaces together, transferring the image to the paper. Previously the printing plate and paper needed to make perfect contact but here the soft blanket can pick up and deposit ink much better than a hard surface, creating impressions on almost any material with greater fidelity. Even though the first offset press was built in 1904, the method only became popular after 1951 when an easy to use, storable, photosensitive aluminum litho-plate was developed. Offset lithography quickly became the standard in photochrome postcard production. Nearly all postcards produced today are made through process printing on offset lithography presses, though they have largely been adapted to digital technology. Lithography is a method of printing using a metal plate with a completely smooth surface. In modern lithography the image is made of a polymer coating applied to a flexible aluminium plate.
Mechanically produced packaging has been, used in printing technology for the last hundred years. As new technology has emerged, modern packaging, printed material and pulp based mediums are now sealed with a clear varnish or sealant. The concept of the sealant is to seal any ink to the surface of printed medium.
Most inks have a low threshold for being rubbed off or smudged. They are also susceptible to moisture and have limited luminescence. The sealing coat prevents the ink from being rubbed off, reduces smudging, and helps to brighten up the inks. Sealants are all applied post production. Any other process that includes additives in the pulping process is as a pre-treatment.
There are three distinct types of sealant: Hydrocarbon oil phase, Aqueous phase, and Poly acrylic. All of them are focused on pre treating the paper or packaging board for the purpose of protecting the surface of the paper or board and making them free from contamination prior to printing. A small number claim residual activity by the use of preservatives placed in the pulp prior to formation into board or paper stock. These are specialist products commanding a premium price and have very specific applications.
The printing process is a method of placing ink on to a surface. The use of a sealant or varnish placed on to a printed surface is designed to fulfill a number of purposes. It is designed to increasing the speed of printing to allow for the sheets to be printed on both sides to improve the finish of the printed medium and to protect the ink from rub off or smudging.
Presently there are no print finishes designed for creating an antimicrobial print finish used in packaging construction or in the print finishing industry.